I'm not experienced in level design either. But the most obvious thing would be to add a layer of blurness for the outside of the playing field. There are many ways to approach this, so I recommend you to find your own solutions which could be more suitable than someone else telling you.
I mean all the videos and courses out there are aiming at the general areas and tried to cover as much grounds as they could. So it's a good idea to try and personalize your games.